Conventionally, this kind of a flexible arm is known as an arrangement provided with discs with curved surfaces arranged in series and wires, cables or the like attached to the discs to transmit power to the respective discs (e.g., Japanese Patent Publication No. 59-21756) or an arrangement provided with torsion plates for holding discs and transmitting power thereto (e.g., specifications of Sweden Patents No. 7902366-9 and No. 8001998-7).
Although the arm of a conventional robot generally moves vertically and horizontally and rotates, the above conventional flexible arm has a feature in that it can be curved and bent or moved in a direction opposite to a robot standing direction since the respective discs have curved surfaces.
As shown in FIGS. 1 and 2, in the above conventional flexible arm, a means for holding the respective discs comprises a minimum unit composed of four discs a, one support plate b, four torsion plates c and bushes e through which wires d pass. This minimum unit is such that the bushes e are fixed to the support plate b by spot welding or rivets, the torsion plate c and the disc a are integrally overlapped on each side of the support plate b and fixed thereto by spot welding or rivets, and each of the remaining two discs a is integrally fixed to each side of the two overlapped torsion plates c by spot welding or rivets. Thus an element fixed to the support plate b side and an element fixed to the two torsion plate sides are arranged in such a manner that they are brought into contact with each other and the adjacent torsion plates are joined to each other at the outer peripheral portions thereof by spot welding or rivets.
With the above conventional arrangement, there is a problem in that the torsion plates are damaged or the surfaces where the discs are in contact are worn and made in a shape which does not have a prescribed curvature since a strong tensile strength or a compressing force is applied to an actuating device for transmitting force such as wires, cables or the like as well as to the above respective discs and the plates for supporting the discs, and thus the flexible arm cannot effect a smooth curving action.
In addition, there is also a problem in that when the tensile strength or the compression force is transmitted through the actuating device, the extreme end of the flexible arm is difficult to locate at a target position due to reactions from the respective discs and the support plates of the discs, and thus positioning accuracy is decreased.